Don’t go through agencies—they charge outrageous fees! And watch out for "list sellers" (they’ll ask you to open a PAID file just to access a list of... nonexistent apartments).
Look for private listings:
- www.pap.fr
- www.leboncoin.fr
- www.souslouer.com (free sign-up to get advertisers’ contact details)
- www.recherche-colocation.com (free sign-up to message advertisers)
- www.colocation.fr (careful—you have to pay to see advertisers’ contact details on this site), but they organize the famous "Thursday Flat-Sharing Day" in Paris:
http://www.colocation.fr/pages/jeudi.phpThese are the sites that helped me the most for finding housing in Paris, and I actually found my place through a Leboncoin ad. There are others, of course.
Normally: 1 month’s deposit, even for furnished places, but many ask for 2 months (the max!). 3 months is illegal—don’t accept it.
Make sure to ask if the place is officially registered by the landlord and if you’re eligible for housing benefits (APL). Depending on your income, CAF can pay up to 200 € in housing aid.
Good luck! (You’ll need it)